"You used to come to see me."
Translation:Tu venais me voir.
This sentence does not have an auxiliary verb.
What is has is two verbs, the second of which is in the infinitive, exactly the same as in English:
"You used to come to see me" = "Tu venais me voir".
In this kind of construction, the object pronoun ("me" in this case) comes before the infinitive.
Venais is past imperfect tense that indicates a past action that was continuing, long-lasting, repeated, habitual, and/or ongoing. It is often translated into English were coming, would come, or used to come.
It is different from the passé composé tense, as venu which indicates short-lasting, one-time past action. It is usually translated as came or has come.
Venais ( main verb venir = to come) is the past imperfect conjugation of verb venir with TU and JE. Tu venais = you used to come. Or can be translated as you were coming. ....Other conjugations for venir in past imperfect are... Je venais.. Tu venais.. Il/ Elle/on venait... Vous veniez... Nous venions... Ils/Elles venaient.